scholarly journals Low intrinsic efficacy for G protein activation can explain the improved side effect profiles of new opioid agonists

2020 ◽  
Vol 13 (625) ◽  
pp. eaaz3140 ◽  
Author(s):  
Alexander Gillis ◽  
Arisbel B. Gondin ◽  
Andrea Kliewer ◽  
Julie Sanchez ◽  
Herman D. Lim ◽  
...  
Keyword(s):  
G Protein ◽  
Side Effect ◽  
Opioid Analgesics ◽  
Receptor Activation ◽  
Alternative Mechanism ◽  
Protein Activation ◽  
Biased Agonism ◽  
Opioid Ligands ◽  
Intrinsic Efficacy ◽  
Respiratory Depressant

Biased agonism at G protein–coupled receptors describes the phenomenon whereby some drugs can activate some downstream signaling activities to the relative exclusion of others. Descriptions of biased agonism focusing on the differential engagement of G proteins versus β-arrestins are commonly limited by the small response windows obtained in pathways that are not amplified or are less effectively coupled to receptor engagement, such as β-arrestin recruitment. At the μ-opioid receptor (MOR), G protein–biased ligands have been proposed to induce less constipation and respiratory depressant side effects than opioids commonly used to treat pain. However, it is unclear whether these improved safety profiles are due to a reduction in β-arrestin–mediated signaling or, alternatively, to their low intrinsic efficacy in all signaling pathways. Here, we systematically evaluated the most recent and promising MOR-biased ligands and assessed their pharmacological profile against existing opioid analgesics in assays not confounded by limited signal windows. We found that oliceridine, PZM21, and SR-17018 had low intrinsic efficacy. We also demonstrated a strong correlation between measures of efficacy for receptor activation, G protein coupling, and β-arrestin recruitment for all tested ligands. By measuring the antinociceptive and respiratory depressant effects of these ligands, we showed that the low intrinsic efficacy of opioid ligands can explain an improved side effect profile. Our results suggest a possible alternative mechanism underlying the improved therapeutic windows described for new opioid ligands, which should be taken into account for future descriptions of ligand action at this important therapeutic target.

scholarly journals Re-evaluating how low intrinsic efficacy and apparent bias for G protein activation relates to the improved side effect profiles of new opioid agonists

2020 ◽  
Author(s):  
Edward L. Stahl ◽  
Laura M. Bohn
Keyword(s):  
G Protein ◽  
Therapeutic Window ◽  
G Protein Signaling ◽  
Protein Signaling ◽  
Protein Activation ◽  
Biased Agonism ◽  
Intrinsic Efficacy ◽  
Cellular Environment ◽  
G Protein Activation ◽  
G Protein Coupled

AbstractIn a recent report by Gillis et al., 2020 (1), it was suggested that low intrinsic agonism, and not biased agonism, leads to an improvement in the separation of potency in opioid-induced respiratory suppression versus antinociception. Although the compounds that were tested have been shown to display G protein signaling bias in prior publications, the authors conclude that since they cannot detect biased agonism in their cellular signaling studies the compounds are therefore not biased agonists. Rather, they conclude that it is low intrinsic efficacy that leads to the therapeutic window improvement. Intrinsic efficacy is the extent to which an agonist can stimulate a G protein-coupled receptor (GPCR) response in a system. The designation of full agonist is made to compounds that produce the highest observable activation in a system (maximum intrinsic efficacy); agonists producing some fraction of that response are considered partial agonists. The maximum response window is determined by the cellular environment, receptor and effector expression levels, and the amplification readout of the system. Biased agonism takes into consideration not only intrinsic efficacy, but also potency (concentration required to reach half maximal efficacy) of an agonist in an assay. Herein, the data published in the aforementioned manuscript was used to rederive the intrinsic efficacy and bias factors as ΔΔlog(τ/KA) and ΔΔlog(Emax/EC50). Based on this reanalysis, the data does not support the conclusion that biased agonism, favoring G protein signaling, was not present. Further, these observations agree with prior studies wherein oliceridine, PZM21 and SR-17018 were first described as biased agonists with improvement in antinociception over respiratory suppression in mice. Therefore, introducing G protein signaling bias may be a means to improve opioid analgesia while avoiding certain undesirable side effects.

scholarly journals Evaluation of G protein bias and β-arrestin 2 signaling in opioid-induced respiratory depression.

2021 ◽  
Author(s):  
Jordan T. Bateman ◽  
Erica S. Levitt
Keyword(s):  
Recent Work ◽  
G Protein ◽  
Respiratory Depression ◽  
G Proteins ◽  
Side Effect ◽  
Opioid Analgesics ◽  
Substantial Evidence ◽  
Intrinsic Efficacy ◽  
Protein Versus

Respiratory depression is a potentially fatal side effect of opioid analgesics and major limitation to their use. G-protein-biased opioid agonists have been proposed as "safer" analgesics with less respiratory depression. These agonists are biased to activate G proteins rather than β-arrestin signaling. Respiratory depression has been shown to correlate with both G-protein bias and intrinsic efficacy, and recent work has refuted the role of β-arrestin signaling in opioid-induced respiratory depression. In addition, there is substantial evidence that G-proteins do, in fact, mediate respiratory depression by actions in respiratory-controlling brainstem neurons. Based on these studies, we provide the perspective that protection from respiratory depression displayed by newly developed G-protein biased agonists is due to factors other than G-protein versus arrestin bias.

scholarly journals β2-adrenoceptor ligand efficacy is tuned by a two-stage interaction with the Gαs C terminus

2021 ◽  
Vol 118 (11) ◽  
pp. e2017201118
Author(s):  
Keehun Kim ◽  
Shayla Paulekas ◽  
Fredrik Sadler ◽  
Tejas M. Gupte ◽  
Michael Ritt ◽  
...  
Keyword(s):  
G Protein ◽  
Dynamic Range ◽  
Receptor Activation ◽  
Activation Mechanism ◽  
Two Stage ◽  
Protein Activation ◽  
Intrinsic Efficacy ◽  
C Terminus ◽  
G Protein Activation ◽  
Structural Determinant

Classical pharmacological models have incorporated an “intrinsic efficacy” parameter to capture system-independent effects of G protein–coupled receptor (GPCR) ligands. However, the nonlinear serial amplification of downstream signaling limits quantitation of ligand intrinsic efficacy. A recent biophysical study has characterized a ligand “molecular efficacy” that quantifies the influence of ligand-dependent receptor conformation on G protein activation. Nonetheless, the structural translation of ligand molecular efficacy into G protein activation remains unclear and forms the focus of this study. We first establish a robust, accessible, and sensitive assay to probe GPCR interaction with G protein and the Gα C terminus (G-peptide), an established structural determinant of G protein selectivity. We circumvent the need for extensive purification protocols by the single-step incorporation of receptor and G protein elements into giant plasma membrane vesicles (GPMVs). We use previously established SPASM FRET sensors to control the stoichiometry and effective concentration of receptor–G protein interactions. We demonstrate that GPMV-incorporated sensors (v-SPASM sensors) provide enhanced dynamic range, expression-insensitive readout, and a reagent level assay that yields single point measurements of ligand molecular efficacy. Leveraging this technology, we establish the receptor–G-peptide interaction as a sufficient structural determinant of this receptor-level parameter. Combining v-SPASM measurements with molecular dynamics (MD) simulations, we elucidate a two-stage receptor activation mechanism, wherein receptor–G-peptide interactions in an intermediate orientation alter the receptor conformational landscape to facilitate engagement of a fully coupled orientation that tunes G protein activation.

scholarly journals Biased Opioid Ligands

Molecules ◽  
2020 ◽  
Vol 25 (18) ◽  
pp. 4257 ◽  
Author(s):  
Abdelfattah Faouzi ◽  
Balazs R. Varga ◽  
Susruta Majumdar
Keyword(s):  
G Protein ◽  
Opioid Receptor ◽  
Opioid Receptors ◽  
Signal Transduction Pathway ◽  
Opioid Peptide ◽  
Nop Receptor ◽  
Biased Agonism ◽  
Opioid Ligands ◽  
Substance Abuse Disorders ◽  
Δ Opioid Receptor

Achieving effective pain management is one of the major challenges associated with modern day medicine. Opioids, such as morphine, have been the reference treatment for moderate to severe acute pain not excluding chronic pain modalities. Opioids act through the opioid receptors, the family of G-protein coupled receptors (GPCRs) that mediate pain relief through both the central and peripheral nervous systems. Four types of opioid receptors have been described, including the μ-opioid receptor (MOR), κ-opioid receptor (KOR), δ-opioid receptor (DOR), and the nociceptin opioid peptide receptor (NOP receptor). Despite the proven success of opioids in treating pain, there are still some inherent limitations. All clinically approved MOR analgesics are associated with adverse effects, which include tolerance, dependence, addiction, constipation, and respiratory depression. On the other hand, KOR selective analgesics have found limited clinical utility because they cause sedation, anxiety, dysphoria, and hallucinations. DOR agonists have also been investigated but they have a tendency to cause convulsions. Ligands targeting NOP receptor have been reported in the preclinical literature to be useful as spinal analgesics and as entities against substance abuse disorders while mixed MOR/NOP receptor agonists are useful as analgesics. Ultimately, the goal of opioid-related drug development has always been to design and synthesize derivatives that are equally or more potent than morphine but most importantly are devoid of the dangerous residual side effects and abuse potential. One proposed strategy is to take advantage of biased agonism, in which distinct downstream pathways can be activated by different molecules working through the exact same receptor. It has been proposed that ligands not recruiting β-arrestin 2 or showing a preference for activating a specific G-protein mediated signal transduction pathway will function as safer analgesic across all opioid subtypes. This review will focus on the design and the pharmacological outcomes of biased ligands at the opioid receptors, aiming at achieving functional selectivity.

scholarly journals Agonist-induced formation of unproductive receptor-G12complexes

2020 ◽  
Vol 117 (35) ◽  
pp. 21723-21730
Author(s):  
Najeah Okashah ◽  
Shane C. Wright ◽  
Kouki Kawakami ◽  
Signe Mathiasen ◽  
Joris Zhou ◽  
...  
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Receptor Activation ◽  
Receptor Internalization ◽  
Protein Association ◽  
Protein Activation ◽  
Protein Receptor ◽  
G Protein Activation

G proteins are activated when they associate with G protein-coupled receptors (GPCRs), often in response to agonist-mediated receptor activation. It is generally thought that agonist-induced receptor-G protein association necessarily promotes G protein activation and, conversely, that activated GPCRs do not interact with G proteins that they do not activate. Here we show that GPCRs can form agonist-dependent complexes with G proteins that they do not activate. Using cell-based bioluminescence resonance energy transfer (BRET) and luminescence assays we find that vasopressin V2receptors (V2R) associate with both Gsand G12heterotrimers when stimulated with the agonist arginine vasopressin (AVP). However, unlike V2R-Gscomplexes, V2R-G12complexes are not destabilized by guanine nucleotides and do not promote G12activation. Activating V2R does not lead to signaling responses downstream of G12activation, but instead inhibits basal G12-mediated signaling, presumably by sequestering G12heterotrimers. Overexpressing G12inhibits G protein receptor kinase (GRK) and arrestin recruitment to V2R and receptor internalization. Formyl peptide (FPR1 and FPR2) and Smoothened (Smo) receptors also form complexes with G12that are insensitive to nucleotides, suggesting that unproductive GPCR-G12complexes are not unique to V2R. These results indicate that agonist-dependent receptor-G protein association does not always lead to G protein activation and may in fact inhibit G protein activation.

Biased Agonism as an Emerging Strategy in the Search for Better Opioid Analgesics

2020 ◽  
Vol 27 (9) ◽  
pp. 1562-1575 ◽  
Author(s):  
Justyna Piekielna-Ciesielska ◽  
Karol Wtorek ◽  
Anna Janecka
Keyword(s):  
Opioid Receptor ◽  
Current Knowledge ◽  
Opioid Analgesics ◽  
New Approach ◽  
Biased Agonism ◽  
Drug Candidates ◽  
Opioid Ligands ◽  
Receptor Profile ◽  
Novel Drug ◽  
Opioid Receptor Agonists

Morphine and related drugs that act through activating opioid receptors are the most effective analgesics for the relief of severe pain. They have been used for decades, despite the range of unwanted side effects that they produce, as no alternative has been found so far. The major goal of opioid research is to understand the mechanism of action of opioid receptor agonists and to improve the therapeutic utility of opioid drugs. In the search for safer and more potent analgesics, analogs with mixed opioid receptor profile gained a lot of interest. However, recently the concept of biased agonism, that highlights the fact that some ligands are able to differentially activate receptor downstream pathways, became a new approach in the design of novel drug candidates for clinical application. In this review, we summarize current knowledge on the development of opioid ligands of peptide and nonpeptide structure, showing how much opioid pharmacology evolved in recent years.

scholarly journals A Dynamic, Split-Luciferase-Based Mini-G Protein Sensor to Functionally Characterize Ligands at All Four Histamine Receptor Subtypes

2020 ◽  
Vol 21 (22) ◽  
pp. 8440
Author(s):  
Carina Höring ◽  
Ulla Seibel ◽  
Katharina Tropmann ◽  
Lukas Grätz ◽  
Denise Mönnich ◽  
...  
Keyword(s):  
G Protein ◽  
Protein Interactions ◽  
Signal Amplitude ◽  
Histamine Receptor ◽  
Receptor Activation ◽  
Functional Assay ◽  
Receptor Subtypes ◽  
Protein Activation ◽  
Drug Candidates ◽  
Specific Effects

In drug discovery, assays with proximal readout are of great importance to study target-specific effects of potential drug candidates. In the field of G protein-coupled receptors (GPCRs), the determination of GPCR-G protein interactions and G protein activation by means of radiolabeled GTP analogs ([35S]GTPγS, [γ-32P]GTP) has widely been used for this purpose. Since we were repeatedly faced with insufficient quality of radiolabeled nucleotides, there was a requirement to implement a novel proximal functional assay for the routine characterization of putative histamine receptor ligands. We applied the split-NanoLuc to the four histamine receptor subtypes (H1R, H2R, H3R, H4R) and recently engineered minimal G (mini-G) proteins. Using this method, the functional response upon receptor activation was monitored in real-time and the four mini-G sensors were evaluated by investigating selected standard (inverse) agonists and antagonists. All potencies and efficacies of the studied ligands were in concordance with literature data. Further, we demonstrated a significant positive correlation of the signal amplitude and the mini-G protein expression level in the case of the H2R, but not for the H1R or the H3R. The pEC50 values of histamine obtained under different mini-G expression levels were consistent. Moreover, we obtained excellent dynamic ranges (Z’ factor) and the signal spans were improved for all receptor subtypes in comparison to the previously performed [35S]GTPγS binding assay.

scholarly journals Biased versus Partial Agonism in the Search for Safer Opioid Analgesics

Molecules ◽  
2020 ◽  
Vol 25 (17) ◽  
pp. 3870 ◽  
Author(s):  
Joaquim Azevedo Neto ◽  
Anna Costanzini ◽  
Roberto De Giorgio ◽  
David G. Lambert ◽  
Chiara Ruzza ◽  
...  
Keyword(s):  
Side Effects ◽  
G Protein ◽  
Side Effect ◽  
Gene Knockout ◽  
Abuse Liability ◽  
Current Data ◽  
Genetically Engineered ◽  
Intrinsic Activity ◽  
Prolonged Treatment ◽  
Biased Agonism

Opioids such as morphine—acting at the mu opioid receptor—are the mainstay for treatment of moderate to severe pain and have good efficacy in these indications. However, these drugs produce a plethora of unwanted adverse effects including respiratory depression, constipation, immune suppression and with prolonged treatment, tolerance, dependence and abuse liability. Studies in β-arrestin 2 gene knockout (βarr2(−/−)) animals indicate that morphine analgesia is potentiated while side effects are reduced, suggesting that drugs biased away from arrestin may manifest with a reduced-side-effect profile. However, there is controversy in this area with improvement of morphine-induced constipation and reduced respiratory effects in βarr2(−/−) mice. Moreover, studies performed with mice genetically engineered with G-protein-biased mu receptors suggested increased sensitivity of these animals to both analgesic actions and side effects of opioid drugs. Several new molecules have been identified as mu receptor G-protein-biased agonists, including oliceridine (TRV130), PZM21 and SR–17018. These compounds have provided preclinical data with apparent support for bias toward G proteins and the genetic premise of effective and safer analgesics. There are clinical data for oliceridine that have been very recently approved for short term intravenous use in hospitals and other controlled settings. While these data are compelling and provide a potential new pathway-based target for drug discovery, a simpler explanation for the behavior of these biased agonists revolves around differences in intrinsic activity. A highly detailed study comparing oliceridine, PZM21 and SR–17018 (among others) in a range of assays showed that these molecules behave as partial agonists. Moreover, there was a correlation between their therapeutic indices and their efficacies, but not their bias factors. If there is amplification of G-protein, but not arrestin pathways, then agonists with reduced efficacy would show high levels of activity at G-protein and low or absent activity at arrestin; offering analgesia with reduced side effects or ‘apparent bias’. Overall, the current data suggests—and we support—caution in ascribing biased agonism to reduced-side-effect profiles for mu-agonist analgesics.

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